Hearing aids to be worn in the ear normally have a microphone directed towards the outside in the ear, a loudspeaker directed towards the interior of the ear, amplifying electronics and a replaceable battery for operation, all said electronic components being located in a shaped member, whose shape is to a greater or lesser extent adapted to the shape of the auditory canal and is worn in the latter. In order that the hearing aid can be comfortably worn and therefore fulfill its function in an optimum manner, various demands are made on the shaped member, which it fulfills to a greater or lesser extent as a function of the construction. These requirements are essentially as follows:
The shaped member must fit well in the auditory canal, so that it has a good position and is still comfortable. PA1 The shaped member must be easily insertable into and removable from the auditory canal. PA1 The shaped member must permit pressure compensation in the auditory canal, despite its good fit. PA1 The shaped member must prevent feedback of the sound produced by the loudspeaker to the microphone. PA1 The shaped member must be skin-compatible, must in particular permit ventilation of the skin of the auditory canal and must not give rise to the exudation of perspiration and earwax. PA1 The shaped member must be insensitive to the exudations of the auditory canal and easily cleaned with respect thereto and must in particular protect the electronic components of the hearing aid from such exudations.
Apart from these requirements relating to the function of the hearing aid and its wearing comfort, there are economic requirements to the effect that the shaped member must be easy to manufacture. It could additionally be desirable for economic reasons for the electronic components to be accessibly integrated into the hearing aid, so that they can be replaced.
The above requirements are satisfied to varying degrees by known hearing aids worn in the ear. Some of them will be briefly described and compared with the above list of requirements.
The most frequently used method for the manufacture of hearing aids to be worn in the ear is performed by a hearing aid advisor, who simultaneously investigates the hearing weaknesses of the potential user, and produces a silicone molding or casting of the auditory canal, on the basis of which is produced a transparent, positive model of the auditory canal. From that model is molded a plastics material polymerizable with the aid of light, which hardens from the outside to the inside up to a given layer thickness. This leads to a hollow shaped member, into which the electronic components of the hearing aid are fitted and towards the interior of the ear there is at least one opening for the loudspeaker and for a pressure compensating channel. Adjacent the outlet of the auditory canal the shaped member is closed with a cover, which contains an opening for the pressure compensating channel and a separate compartment for a replaceable battery.
The thus manufactured hearing aid has a shaped member with a very good fit, but which covers the skin of the auditory canal without interruption in such a way that there can be no question of ventilation. This unavoidably leads to increased exudation of perspiration and earwax. The part of the auditory canal left free between the eardrum and hearing aid is open to the outside through the pressure compensating channel, so that pressure compensation can take place and moisture can also escape. However, the pressure compensating channel can increase the feedback between the loudspeaker and the microphone.
A further disadvantage of this hearing aid is that the openings to the loudspeaker and the pressure compensating channel can become easily blocked with earwax and same can also be covered with a liquid-impermeable, but gas-permeable diaphragm, as proposed in European patent application 310,866 (published 12.4.1989).
The described hearing aid manufacturing method is complicated, because the shaped member must be molded in several positive-negative stages and because the manufacturing stages are such that they cannot be performed by the hearing aid advisor. Thus, the manufacturer of the hearing aid must deal with the individual production of user-specific equipment.
In order to simplify the manufacturing methods various proposals have been made. Thus, e.g. according to U.S. Pat. No. 4,962,537, it is proposed that the shaped member be in the form of a double-wall bag of a flexible material, a hardening plastic mass being directly pressed into the user's ear between the two walls. This method saves a few steps in the manufacture, but the molded shaped member must still be reworked, in particular it is necessary to subsequently make openings for a pressure compensating channel and for the loudspeaker and it is doubtful whether this can be done by the hearing aid advisor.
The same applies with respect to the hearing aid according to International patent application W092/03894, whose shaped member is directly molded in the auditory canal.
The two aforementioned manufacturing methods are admittedly simpler than the first-described method, but do not improve the disadvantages with respect to skin contact and feedback. This also applies with regards to the hearing aid of U.S. Pat. No. 4,834,211, in which the shaped member is constituted by a balloon surrounding the electronic components of the hearing aid and which during each insertion into the ear is inflated with a corresponding pump. With such a hearing aid the skin contact and feedback are not improved and there can be no question of simple insertion into the ear.